Masterpact M Replacement Trip Unit (dual Hz frequency*)

The Amp Safe Pro is the ONLY trip unit specifically designed and developed to precisely emulate the Masterpact STR DINF functions and curves (with added standard features such as trip history, neutral overcurrent protection and sluggish breaker options).This contrasts sharply with competing units, which adapt an existing two-part protection device designed for open frame breakers, by packaging the two parts into a single enclosure, capable of being fitted to the Masterpact M and MP breaker.

For a FREE Evaluation call:

01299 251 758

Since April 2015, the Amp-Safe-Pro has also been available as a fixed, 60Hz unit. We can supply this trip unit (indicated by a red facia), but this is only suited to countries which use a 60Hz system and will not function correctly if used within a 50Hz system.Our standard (green facia) Amp Safe Pro is dual frequency and UL/CE approved. It is specifically produced to operate in the United Kingdom and Europe but is suitable for worldwide service. Both the fixed and duo frequency models come with a two year warranty.


Trip unit

The Amp-Safe-Pro™ is now UL and CE
listed for use in Masterpact M Series Breakers!


Required Alarm

A new feature; the ability to measure the breaker opening speed on the “first operation”. Also incorporates self test feature & more importantly uses continual loop feedback to the mitop*.



The Amp-Safe-Pro™ is now UL and CE
listed for use in Masterpact M Series Breakers!

*The mitop coil is the small actuator device that trips the breaker in an event of a fault, so monitoring of this circuit is extremely important to the safe & correct operation of the protection device.

Standard trip functions include:

(These will vary depending on the STR type selected)

  • Long-Time
  • Short-Time
  • Instantaneous
  • Residual Ground Fault
  • Ground Return Ground Fault
  • Instantaneous on Closing (DINF)
  • Over Temperature Trip

All of the settings are protected by a security
code to prevent unauthorized modifications.

The Amp-Safe-Pro can be programmed one of two ways. The front of the unit has an OLED display that is easy to read in either low or high ambient light. The buttons on the front of the unit are “smart” buttons that change their functions based on the displayed information.The second way to program the Amp-Safe-Pro is using the USB port on the front of the unit. Using a GUI program all of the settings can be programmed on a computer and pushed the Amp-Safe-Pro. The same program can be used to pull commissioning and trip event data from the unit.

The Amp-Safe-Pro has a mechanical pop out trip indicator on the front of the unit that mimics the functionality of the original unit.

There is also a SELF-TEST OK Led, PRE-TRIP LED, QUICK-TRIP switch and an easily accessible battery LI-Ion battery. The SELF-TEST OK LED indicates a properly operating trip unit. The PRE-TRIP LED indicates a pending trip.

The QUICK-TRIP switch activates QT-Instantaneous and QT-Ground Fault settings in the trip unit to reduce arc flash potential. Connections for a remote QUICK-TRIP switch and indicating light are available.

The battery in the Amp-Safe-Pro is only used to power the trip to review trip data or change settings on the when no power is provided from the CT’s. The battery is not used for any of the protective functions of the Amp-Safe-Pro. The battery is also not used to save the last trip data or settings. All of this data is saved in non-volatile memory.

The trip unit saves the type of trip, phase and ground currents and date/time for the last 8 trip events. There is also a trip counter that provides the number of trips by trip function.

More on trip units for low voltage AC and DC circuit breakers


Installation Manual

Please click here to download the installation manual as a PDF file

Data Sheet

Please click here to download the data sheet as a PDF file

AMP-SAFE-PROTM trip unit

Results of test of DINF instantaneous trip function confirming proper operation.Please click here to download a PDF file